Spinal stenosis typically occurs when the spinal cord, cauda equina and/or nerve root(s) are impinged by one or more tissues in the spine, such as a buckled or thickened ligamentum flavum. Impingement of neural and/or neurovascular tissue in the spine by a buckled or thickened ligamentum flavum may cause pain, numbness and/or loss of strength or mobility in one or both of a patient's lower limbs and/or of the patient's back.
In lumbar spinal stenosis (LSS), the space around the spinal cord becomes narrow, thus compressing the spinal cord and the nerve roots. This causes back pain with neurogenic claudication, i.e., pain, numbness, or weakness in the legs that worsens with standing or walking and is alleviated with sitting or leaning forward. Compression of neural elements generally occurs as a result of hypertrophied facet or ligamentum flavum hypertrophy. LSS is one of the most common reasons for back surgery and the most common reason for lumbar spine surgery in adults over 65 years of age. Patients suffering from spinal stenosis are typically first treated with conservative approaches such as exercise therapy, analgesics, anti-inflammatory medications, and epidural steroid injections. When these conservative treatment options fail and symptoms are severe, surgery may be required to remove impinging tissue and decompress the impinged nerve tissue.
The source of most cases of lumbar spinal stenosis is thickening of the ligamentum flavum. Spinal stenosis may also be caused by subluxation, facet joint hypertrophy, osteophyte formation, underdevelopment of spinal canal, spondylosis deformans, degenerative intervertebral discs, degenerative spondylolisthesis, degenerative arthritis, ossification of the vertebral accessory ligaments and the like. A less common cause of spinal stenosis, which usually affects patients with morbid obesity or patients on oral corticosteroids, is excess fat in the epidural space. The excessive epidural fat compresses the dural sac, nerve roots and blood vessels contained therein and resulting in back and leg pain and weakness and numbness of the legs. Spinal stenosis may also affect the cervical and, less commonly, the thoracic spine.
Patients suffering from spinal stenosis are typically first treated with exercise therapy, analgesics and anti-inflammatory medications. These conservative treatment options frequently fail. If symptoms are severe, surgery is required to decompress the canal and nerve roots.
To correct stenosis in the lumbar region, an incision is made in the back and the muscles and supporting structures are stripped away from the spine, exposing the posterior aspect of the vertebral column. The thickened ligamentum flavum is then exposed by removal of the bony arch (lamina) covering the back of the spinal canal (laminectomy). The thickened ligament can then be excised with sharp dissection with a scalpel or punching instruments such as a Kerison punch that is used to remove small chips of tissue. The procedure is performed under general anesthesia. Patients are usually admitted to the hospital for approximately five to seven days depending on the age and overall condition of the patient. Patients usually require between six weeks and three months to recover from the procedure. Many patients need extended therapy at a rehabilitation facility to regain enough mobility to live independently.
Much of the pain and disability after an open laminectomy is due to the tearing and cutting of the back muscles, blood vessels and supporting ligaments and nerves that occurs during the exposure of the spinal column. Also, because these spine stabilizing back muscles and ligaments are stripped and cut off, the spine these patients frequently develop spinal instability post-operatively.
Minimally invasive techniques result in less post-operative pain and faster recovery compared to traditional open surgery. Percutaneous interventional spinal procedures can be performed with local anesthesia, thereby sparing the patient the risks and recovery time required with general anesthesia. Another advantage is that there is less damage to the paraspinal muscles and ligaments with minimally invasive techniques reducing pain and preserving these important stabilizing structures.
Various techniques for minimally invasive treatment of the spine are known. Microdiscectomy is performed by making a small incision in the skin and deep tissues to create a portal to the spine. A microscope is then used to aid in the dissection of the adjacent structures prior to discectomy. The recovery period for this procedure is much shorter than traditional open discectomies. Percutaneous discectomy devices with fluoroscopic guidance have been used successfully to treat disorders of the disc, but not to treat spinal stenosis or the ligamentum flavum directly. Arthroscopy or direct visualization of the spinal structures using a catheter or optical system have also been proposed to treat disorders of the spine, including spinal stenosis. However, these devices still use miniaturized standard surgical instruments and direct visualization of the spine, similar to open surgical procedures. These devices and techniques are limited by the small size of the canal and these operations are difficult to perform and master. Also, these procedures are painful and often require general anesthesia. The arthroscopy procedures are time consuming and the fiber optic systems are expensive to purchase and maintain. In addition, because the nerves of the spine pass through the core of the spine directly in front of the ligamentum flavum, any surgery, regardless of whether is open or percutaneous, includes a risk of damage to those nerves.
It is desirable to provide a method and device for treating spinal stenosis and other spinal disorders without requiring open surgery. It is further desired to provide a system that protects the thecal sac or dura containing the spinal nerves while the ligamentum flavum is cut. Accordingly, there is a need for devices and methods to provide efficient severing or cutting of tissue that can be used during a minimally invasive procedure and/or during an open surgical procedure, such as, for example, open decompression.